Balloon catheters are commonly used in relatively non-invasive medical procedures for the treatment of heart disease, such as in coronary angiography and percutaneous transluminal coronary angioplasty (PTCA). During such procedures, a balloon catheter is advanced through the vasculature of a patient such that the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
In a typical PTCA procedure, a hollow guiding catheter, a guidewire and a dilation catheter are inserted into the vasculature of a patient. The guiding catheter has a pre-shaped distal tip which is percutaneously introduced into the vasculature and advanced. An operator, such as a surgeon, twists and moves the proximal end of the guiding catheter to advance the distal tip through the aorta. The distal tip reaches the ostium of a diseased coronary artery.
Such medical devices require exacting specifications in order to perform adequately under the rigorous conditions in which they are required to perform. Depending on the end use, such medical devices may be primarily comprised of polymeric materials that are non-thrombogenic, non-immunogenic, flexible, manipulatable, that exhibit both radial and longitudinal strength and/or, in certain applications, and so forth.
Balloon dilatation catheters desirably have strength, softness, flexibility and a thin, low profile which are important for achieving the performance characteristics of folding in an uninflated state, tracking, crossing and recrossing the area of the obstruction or stenosis in a vessel in an uninflated state. However, when balloon dilatation catheters are used in large vessels, such as in the coronary or peripheral systems, the size of the vessels and thus the size of the balloons used to dilate them requires that the balloons have a thicker wall. Thicker walls however, tend to increase the stiffness, and to decrease the ability to track, and to cross and recross, for example.
Thus, inasmuch as there are very few single polymeric materials that provide this combination of characteristics, most medical devices are comprised of more than one polymeric material to provide the desired combination of physical properties. The use of multiple polymeric materials, in turn, requires that the polymeric materials be securely bonded together, through welding or through the use of an adhesive, or other bonding method.
Thus, adhesives or thermal welding are typically employed in several locations of a balloon catheter. For instance, balloon catheters typically have an outer tubular member with a distal extremity terminating within the balloon interior and an inner tubular member with a distal extremity extending through and slightly beyond the distal end of the balloon. The annular space between the inner and outer members defines the inflation lumen in communication with the balloon interior. The integrity of the balloon interior is maintained, thereby enabling the balloon interior to hold inflation media, by fluid tight bonds located at proximal and distal extremities of the balloon which secure the balloon to the outer tubular member and the inner tubular member respectively.
Additionally, it may be desirable to form a guide catheter by bonding together two or more tubular sections in order to achieve a more rigid proximal portion and more flexible distal portion. Thus, when a guide catheter is comprised of more than one generally tubular section, these sections are joined together at joints where the distal end of a first tubular section is affixed to the proximal end of a second tubular section.
Thus, in the manufacture of balloon catheters or guide catheters, a number of techniques may be used to bond the balloon to the catheter shaft, including use of adhesives or thermal bonding, i.e. welding.
During welding operations, it is common to employ a heat shrinkable material as a way to exert a compressive force on the region to be welded. Polyolefin or polytetrafluoroethylene heat shrink are typically used in the manufacture of medical devices as a way to exert force and thermally weld two polymeric materials together. See, for example, commonly assigned U.S. Pat. No. 6,409,863 which is incorporated by reference herein in its entirety.
Using a heat shrink material is accomplished by a multi step process including irradiating the heat shrink and then expanding the material to achieve the required compressive properties typically accomplish this. The heat shrink is then cut in to small rings and placed around the surfaces to be bonded or welded. Placement and orientation of the heat shrink is very important to the production of an acceptable and reproducible bond. Thus, this method is both time consuming and costly. See also commonly assigned U.S. Pat. No. 5,549,552 which is incorporated by reference herein in its entirety.
There remains a need in the art to employ polymeric materials in such a way as to optimize the performance of various components of a catheter device, and for a faster, more economical process for joining various components of a catheter device
Additionally, there remains a specific need in the art for a dilatation balloon catheter which has an improved crossing profile and stenosis recrossing, trackability, and balloon retrieval after deflation.